Long-distance axial trapping with focused annular laser beams.

PloS one

PubMedID: 23505449

Lei M, Li Z, Yan S, Yao B, Dan D, Qi Y, Qian J, Yang Y, Gao P, Ye T. Long-distance axial trapping with focused annular laser beams. PLoS ONE. 2013;8(3):e57984.
Focusing an annular laser beam can improve the axial trapping efficiency due to the reduction of the scattering force, which enables the use of a lower numerical aperture (NA) objective lens with a long working distance to trap particles in deeper aqueous medium. In this paper, we present an axicon-to-axicon scheme for producing parallel annular beams with the advantages of higher efficiency compared with the obstructed beam approach. The validity of the scheme is verified by the observation of a stable trapping of silica microspheres with relatively low NA microscope objective lenses (NA?=?0.6 and 0.45), and the axial trapping depth of 5 mm is demonstrated in experiment.